is a lifeform
of a varity of cold-blooded
vertebrates. They spend part of their time on land but are still bound to immerse themselves in fresh water the other half of their time.
When Counselor Deanna Troi was affected by Barclay's Protomorphosis Syndrome she de-evolved into an amphibian, complete with gills. (TNG: "Genesis")
When Tom Paris underwent a phase of hyper-evolution after reaching Warp 10 he rapidly evolved into an amphibian lifeform. (VOY: "Threshold")
Types of amphibians
Sentient amphibian species